CVE-2025-67725: Tornado is a Python web framework and asynchronous networking library

Q: How do I fix CVE-2025-67725?

tornado: upgrade to 6.5.3. Exact commands for each OS are on this page.

Q: Is CVE-2025-67725 being exploited?

CVE-2025-67725 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2025-67725 affect?

CVE-2025-67725 affects tornado. Severity is high (CVSS 7.5). Tornado is a Python web framework and asynchronous networking library. In versions 6.5.2 and below, a single maliciously crafted HTTP request can block the server's event loop for an extended period, caused by the HTTPHeaders.add method. Th

Q: How urgent is CVE-2025-67725?

Priority 43/100. High severity; Remotely exploitable, no login, no user action

This month

HIGH 7.5REMOTEUPGRADE

CVE-2025-67725 is a high-severity flaw (CVSS 7.5) affecting tornado. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Tornado is a Python web framework and asynchronous networking library. In versions 6.5.2 and below, a single maliciously crafted HTTP request can block the server's event loop for an extended period, caused by the HTTPHeaders.add method. The function accumulates values using string concatenation when the same header name is repeated, causing a Denial of Service (DoS). Due to Python string immutability, each concatenation copies the entire string

Why this priority

High severity
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	7.5 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.6% (top 54%)
CISA exploited list	No
Weakness	CWE-400
Published	2025-12-12
Last modified	2026-10-07

Publisher (CNA): GitHub, Inc. · Vendor: tornadoweb

Last updated 2026-10-07 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2025-12-12 06:15 UTCPublished CVE record published
2026-10-07 20:10 UTCUpdated Record last modified

tornadoweb tornado UPGRADE

Affected: < 6.5.3

Fixed in: 6.5.3

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy tornado || rpm -q tornado || tornado --version

2. UPGRADE to 6.5.3 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade tornado

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade tornado

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2025-67725?

tornado: upgrade to 6.5.3. Exact commands for each OS are on this page.

Is CVE-2025-67725 being exploited?

CVE-2025-67725 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2025-67725 affect?

CVE-2025-67725 affects tornado. Severity is high (CVSS 7.5). Tornado is a Python web framework and asynchronous networking library. In versions 6.5.2 and below, a single maliciously crafted HTTP request can block the server's event loop for an extended period, caused by the HTTPHeaders.add method. Th

How urgent is CVE-2025-67725?

Priority 43/100. High severity; Remotely exploitable, no login, no user action

Software pages

Python vulnerabilities

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References

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